Deparaffinization of tissue by electric field generation and ionization

ABSTRACT

Paraffin-embedded tissue, which may be disposed on a solid substrate, is prepared by a dry technique that removes paraffin from tissue without adding any liquid to the tissue, thereby rendering the tissue substantially free of paraffin. The dry technique may entail applying heat energy to the tissue effective to melt the paraffin and thereby render it flowable, and applying an electric field. The electric field is effective to impart electrical charge to the paraffin and to move the paraffin out from the tissue due to electrical charge repulsion or attraction, which may be assisted by moving an electrode utilized to generate the electric field relative to the paraffin. The electric field, or both the electric field and the heat energy, may be applied until the tissue is substantially free of paraffin.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application Ser. No. 62/415,502, filed Oct. 31, 2016,titled “DEPARAFFINIZATION OF TISSUE BY ELECTRIC FIELD GENERATION ANDIONIZATION,” the content of which is incorporated by reference herein inits entirety.

TECHNICAL FIELD

The present invention generally relates to the removal of paraffin fromparaffin-embedded tissue, such as may be performed, for example, inpreparation for staining tissue for microscopic study. Moreparticularly, the invention relates to the removal of paraffin by way ofa dry technique that does not entail the addition of any liquid. The drytechnique may implement an electric field-based modality in whichelectrical charge is imparted to the paraffin to be removed.

BACKGROUND

In histology and related fields (e.g., histopathology), a biologicalspecimen such as cellular tissue is collected from a human or animal andthen subjected to various processing steps in preparation for beingstored for a potentially long period of time and subsequently examinedby an analytical instrument such as a light microscope or electronmicroscope. A typical preparative process may entail fixing, processing(dehydration and stiffener infiltration), embedding, sectioning, drying,and staining.

As an example, a biopsy or surgical procedure is performed to collecttissue for subsequent study. The collected tissue is then placed in atissue jar containing a chemical fixative such as formalin to stop thenatural degradation process. Fixatives crosslink proteins to therebydestroy the functionality of enzymes that degrade tissue. The tissue jaris then transported to a laboratory for further processing. At thistime, information regarding the tissue may be entered into a laboratoryinformation system (LIS) and the tissue may be given an identificationnumber.

Next, the tissue sample is sent for grossing. A technician (e.g., apathologist or other appropriately trained person such as a pathologyresident or a histology technician) examines the tissue as it wasreceived. The technician may note the size, condition, and anyremarkable features of the tissue, and verbally record observations thatare later entered into the LIS. The technician then selects appropriateportion(s) of the tissue for histological examination. The tissueportion(s) are cut to a size that fits easily within the tissuecassette(s) and preferably smaller than that. The tissue portion(s) areplaced loosely into a tissue cassette that is labeled with a barcodecontaining information associated with the tissue and the tissuecassette is closed to secure the tissue therein. A typical tissuecassette has outer dimensions of about 28.5×41×6.7 millimeters (mm), ahinged lid, and flow-through slots or holes to allow the tissue to beimmersed in liquid while remaining securely contained inside the tissuecassette. The tissue cassette may then be immersed in a fixative bathfor several hours.

The tissue sample is then subjected to processing, which may beautomated using a suitable processing apparatus. The entire goal ofprocessing is to completely dehydrate the tissue so that the tissue canbe infiltrated with paraffin to make it stiff enough to cut later. Thetissue is immersed in alcohol baths of successively increasing alcoholconcentrations, for example a 70% ethanol bath for fifteen minutes,followed by a 90% ethanol bath for fifteen minutes, followed by a seriesof 100% ethanol baths for longer times. Some processors includemicrowave or acoustic methods to speed up the exchange. Next, thedehydrated tissue is immersed in a xylene (or other clearing agent) bathfor twenty minutes to an hour to completely remove the alcohol, as thealcohol is immiscible with paraffin. The last step of processing is toinfiltrate the tissue with melted paraffin (usually at about 60° C.) andthen cool the tissue to room temperature.

The technician then collects all of the closed, barcoded tissuecassettes containing the tissues and brings them to an embeddingstation. The embedding station includes a hot melt gun containing meltedparaffin and a chill plate. The technician opens one cassette andselects a mold that will comfortably fit the tissue inside the tissuecassette. The technician places a small amount of paraffin in the baseof the mold, and then arranges the tissue in the mold as the paraffinsolidifies on the chill plate. Orientation of the tissue matters at thispoint, as the tissue closest to the bottom of the mold will be thetissue that is first cut by a microtome. The technician then fills therest of the mold with melted paraffin. Next, the technician places thebackside of the tissue cassette against the paraffin and may add afurther amount of paraffin. The tissue cassette carries the barcodeinformation and acts at a holder for the tissue block. The technicianthen sets the mold aside until the paraffin hardens, and then removesthe tissue block from the mold. The resulting tissue is referred to asformalin fixed paraffin embedded (FFPE) tissue.

The technician then uses a microtome to section (cut) the tissue blockto obtain one or more thin slices of the stiffened tissue. Usually thethickness of these tissue slices is on the order of 4 to 6 micrometers(μm), although a range of 1 micrometer to 30 micrometers is notuncommon. For mosts staining protocols, the goal is to get across-section of the tissue that is approximately one cell thick.Genomic analysis may have different requirements depending on the amountof tumor in a section. The technician typically starts by trimming awaythe excess paraffin on the top of the tissue block using the microtome.Once the tissue is exposed, the technician cuts several sections, whichtend to form a ribbon. The ribbon is carefully placed in a heated waterbath to flatten both the paraffin and the tissue. The technician thensingulates the ribbon into individual sections and draws up each sectiononto a glass microscope slide. At this point, each slide consists of oneor two or several sections of tissue and paraffin (both the infiltratingparaffin and the embedding paraffin) held onto the slide by surfacetension from a very thin film of water. Each slide is barcoded foridentification.

For most staining protocols, the tissue sections need to be carefullydried on the slide, as it is critical that the sections fully adhere tothe slides. Drying typically entails air-drying the slides for abouttwenty minutes in a vertical orientation to allow the water to flow tothe bottom of the section and then evaporate. This process puts thetissue into direct contact with the glass microscope slide. Next, theslide is baked at about 60° C. Usually the slide is placed flat on a hotplate or in a heated chamber (e.g., an oven) for about twenty minutes toan hour. There are some variants to the heating apparatus available, butall of them essentially involve the use of heated chambers or hot platesin some form. This process of drying and baking is done to ensureadhesion of the tissue to the slide throughout the staining process andpotentially a decade or more of subsequent storage. Tissue thatseparates from the slide is lost, the consequence of which can beserious such as in the case of a patient who experienced surgery toobtain the tissue sample. Tissue adhesion to non-charged slides may beproblematic, however it is routinely performed for H&E stained sections.To help with adhesion, some labs use charged slides so that the negativecharges on the proteins and nucleic acids (deoxyribonucleic acid or DNA,and ribonucleic acid or RNA) of the sample interact with positivelycharged slides. Other labs put an adhesive in the water bath while usingplain glass slides to be sure that the tissues adhere to the slides. Thelength of the drying and baking time varies depending on the subsequentstaining process to be performed. The baking protocol is longer forslides that will be stained for immunohistochemistry (IHC) than for thestandard hematoxylin and eosin (H&E) staining simply because IHC is amore aggressive chemistry and hence increases the likelihood of tissuesections falling off the slides.

After the tissue has been adhered to the slide, the tissue may bestained. There are many kinds of staining. Normally, a tissue block willhave a section mounted on a slide for H&E staining. Hematoxylin stainsnucleic acids blue and thus is useful as a marker of the cellularnucleus. Eosin stains proteins pink and thus is useful as a marker ofcellular membranes, cytoplasm and extracellular matrix. Pathologists useH&E stained slides to look at the morphology of the tissue structure.Often the pathologist can obtain a diagnosis from studying H&E stainedslides alone and does not need any further analysis.

The first step in staining a tissue section is removing the paraffinadhered to the slide and intermixed with the tissue. The traditionalsequence of steps involved in removing the paraffin is essentially theopposite of that described above. The slide is dipped in xylene oranother clearing agent to dissolve the paraffin and remove it. The slideis then placed into a series of ethanol solutions starting with 100%ethanol composition to remove the xylene and moving down to 70%composition to rehydrate the tissue. Other solvents such as isopropylalcohol are also becoming popular although they do not work as well asxylene. Then the slide is placed in deionized water.

After removing the paraffin, the slide is stained. For example, theslide may be placed into a hematoxylin solution to stain the nuclei andthen rinsed. Subsequently, the slide may be placed into an eosinsolution to stain the protein and then rinsed. Next, a mounting solutionis placed over the stained tissue and a thin coverslip (very thin glassor plastic) is placed over the tissue and the edges are bonded. Thecoverslip allows for easier viewing under the microscope.

Some diagnoses require the use of other types of staining. For example,special stains are used to diagnose microbial infections. As anotherexample, IHC is a method of using antibodies to test for the presence ofspecific proteins. It is used to primarily to characterize cancers morespecifically. The staining process is similar to H&E, in that theparaffin needs to be removed and the tissue rehydrated. However, thereis an extra step in which the protein antigen in the tissue is“retrieved” by heating the tissue to perhaps 90° C. in various buffers.Once the antigen is retrieved, the antibody is applied. The slide isthen washed, and a labeling step is performed to apply color to theslide where the antibody has stuck to the tissue.

From the foregoing, it is evident that the processing of collectedtissue for subsequent study involves many steps and a considerableamount of time. Thus, any improvements in such processing that eliminateone or more of these steps and/or reduce the amount of time requiredwould be desirable.

In the case of studying nucleic acids (DNA and RNA), the exposure oftissue to aromatic hydrocarbons in laboratory-grade xylene or xylenesubstitutes is known to cause oxidation of guanosine nucleotides in DNAand RNA. Xylene causes oxidation of guanosine nucleotides in DNA to8-hydroxydeoxyguanosine and in RNA to 8-hydroxyguanosine. Oxidizedguanosine nucleotides may introduce sequencing artifacts or mutationsinto the DNA or RNA that are amplified by the polymerase chain reaction(PCR) typically performed for subsequent genomic analysis. Thus, itwould be desirable to provide a way to remove paraffin from tissuesamples that avoids the use of xylene or xylene substitutes andconsequently avoids oxidative damage to guanosine nucleotides, therebyenabling the extraction from tissues of DNA and RNA of superior quality.Technologies that may benefit from superior nucleic acid qualityinclude, for example, DNA microarrays, NANOSTRING™ assaying techniques,quantitative PCR (qPCR), and next generation sequencing technologies.Another technology that may benefit from better-quality nucleic acid ishybridization of DNA or RNA probes to nucleic acids in the tissue fordetection of mutations by, for example, fluorescence in situhybridization (FISH) and chromogenic in situ hybridization (CISH).

SUMMARY

To address the foregoing problems, in whole or in part, and/or otherproblems that may have been observed by persons skilled in the art, thepresent disclosure provides methods, processes, systems, apparatus,instruments, and/or devices, as described by way of example inimplementations set forth below.

According to one embodiment, a method for preparing a tissue includes:providing a tissue embedded with paraffin; and removing the paraffinfrom the tissue without adding any liquid to the tissue, whereinremoving the paraffin renders the tissue substantially free of paraffin.

According to another embodiment, a method for preparing a tissueincludes: providing a tissue embedded with paraffin; applying heatenergy to the tissue effective to melt the paraffin; applying anelectric field effective to ionize the paraffin and to move the ionizedparaffin out from the tissue due to electrostatic force; and continuingto apply the electric field until the tissue is substantially free ofparaffin.

According to another embodiment, a tissue preparation device includes aheating device configured for applying heat energy according to any ofthe methods disclosed herein.

According to another embodiment, a tissue preparation device includes anelectric field-generating device configured for applying an electricalfield according to any of the methods disclosed herein.

According to another embodiment, a tissue preparation device includes: aheating device configured for applying heat energy to a tissue effectiveto melt paraffin embedded in the tissue; and an electricfield-generating device configured for applying an electrical fieldeffective to ionize the paraffin and to move the ionized paraffin outfrom the tissue due to electrostatic force.

Other devices, apparatus, systems, methods, features and advantages ofthe invention will be or will become apparent to one with skill in theart upon examination of the following figures and detailed description.It is intended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a schematic perspective view of a tissue sample preparationdevice (or paraffin removal device) according to an embodiment.

FIG. 2 is a schematic elevation view of the tissue sample preparationdevice illustrated in FIG. 1, illustrating its operation.

FIG. 3 is a schematic view of a tissue sample preparation deviceaccording to another embodiment.

FIG. 4 is a schematic view of a tissue sample preparation deviceaccording to another embodiment.

DETAILED DESCRIPTION

The present disclosure provides “dry” techniques for removing paraffinfrom paraffin-laden tissue (i.e., an organized ensemble of biologicalcells) as an alternative to conventional “wet” (chemical) techniques. Adry technique as disclosed herein is one that does not involve theaddition of xylene or other liquids to the tissue. Thus, according to anaspect of the present disclosure, a method for preparing aparaffin-laden tissue includes removing the paraffin from the tissuewithout adding any liquid to the tissue, such that removing the paraffinrenders the tissue substantially free of paraffin. In an embodiment,removing the paraffin from the tissue without adding any liquid to thetissue involves applying energy to the paraffin. In one specific yetnon-limiting embodiment, electrical energy and heat energy are appliedto the paraffin. The electrical energy creates an energetic environmentto which the paraffin is exposed, causing the paraffin to become ionizedand thus responsive to the electric field associated with the electricalenergy applied. Consequently, the electrical field can be utilized tomove (e.g., push or pull) the ionized paraffin out from the tissue. Theheat energy is applied to render the paraffin flowable, thusfacilitating movement of the paraffin out from the tissue. Thus,according to another aspect of the present disclosure, a method forpreparing a paraffin-laden tissue includes applying heat energy to thetissue effective to melt the paraffin, and applying an electric fieldeffective to ionize the paraffin and to move the ionized paraffin outfrom the tissue due to electrostatic force. The electric field, or boththe electric field and the heat energy, continue to be applied until thetissue is substantially free of paraffin.

As used herein, the phrase “substantially free of paraffin” may meanthat a tissue subjected to a dry technique for removing paraffin asdisclosed herein thereafter can be successfully stained by routinetechniques (e.g. H&E or FISH), because any residual paraffin (i.e., theparaffin still remaining in the tissue after being subjected to themethod) is too low to interfere with the process of staining. As anotherexample, in a tissue substantially free of paraffin, the residualparaffin may not be visible to the naked (unaided) eye, but may beobserved as a thin film with the use of a microscope, such as forexample a microscope equipped with polarized lenses. As another example,the tissue substantially free of paraffin is stable at room temperaturefor an extended period of time (e.g. overnight) due to the absence ofliquid, and can be readily stained after the extended period of time.

As another example, a tissue “substantially free of paraffin” may referto a tissue that, after being subjected to a dry technique for removingparaffin as disclosed herein, is greater than 98% free of paraffin,i.e., contains less than 2% residual paraffin, or less than 1% residualparaffin, or less than 0.5% residual paraffin, or less than 0.4%residual paraffin, or less than 0.3% residual paraffin, or less than0.2% residual paraffin, or less than 0.1% residual paraffin, or lessthan 0.05% residual paraffin, or less than 0.01% residual paraffin, etc.

As used herein, the phrase “removing substantially all of the paraffin”may mean removing greater than 98% of the original paraffin in a tissue.As examples, the amount of residual paraffin remaining in the tissue(after subjecting the tissue to a dry technique for removing paraffin asdisclosed herein) may be less than 2%, or less than 1%, or less than0.5%, or less than 0.4%, or less than 0.3%, or less than 0.2%, or lessthan 0.1%, or less than 0.05%, or less than 0.01%, etc., of the amountof the original paraffin in the tissue.

A non-limiting example of an embodiment of a dry technique for removingparaffin from tissue, utilizing an electric field modality assisted by aheating modality, will now be described.

FIG. 1 is a schematic perspective view of a tissue preparation device100 according to an embodiment. The device 100 may also be referred toas a paraffin removal device or a tissue deparaffinization device. FIG.1 also illustrates a supported tissue arrangement 104 that includes atissue 108, which may also be referred to as a tissue sample, disposedon an upper surface of a solid substrate 112 (e.g., a microscope slide).The tissue 108 may be adhered to the solid substrate 122, oralternatively may freely rest on the in an unbound manner. For example,the tissue sample 104 may have been collected and processed as describedabove in the background section of the present disclosure. Thus, wheninitially provided for processing by the device 100, the tissue 108 isimpregnated with paraffin. In addition to a slide, other examples ofsolid substrates include, but are not limited to, a plate, a frit,beads, a porous medium, a filter, and a container. The device 100 isconfigured for removing paraffin from a tissue 108, which may be done inpreparation for staining as described above, or for other desiredprocessing or analysis. The substrate 112 may have a higher surfaceenergy than the paraffin and/or the tissue 108, so that after theparaffin is removed the tissue 108 adheres to the substrate 112.

Generally, the device 100 includes an electric field-generating device116, and may further include a heating device 120.

The electric field-generating device 116 includes an electrodearrangement, such as one or more movable first electrodes (or dischargeelectrodes) 124 and one or more (typically stationary) second electrodes(or counter-electrodes) 128, and an appropriate voltage source (orelectrical power supply) 132. The voltage source 132 may be a directcurrent (DC) voltage source or alternating current (AC) voltage source.As an AC voltage source, the voltage source 132 in some embodiments maybe a high-frequency voltage source such as a radio-frequency (RF)voltage source or a microwave-frequency voltage source. At least thefirst electrode 124 is in electrical communication with the voltagesource 132. Depending on the embodiment, the second electrode 128 may bein electrical communication with the voltage source 132 or may becoupled to electrical ground. In one non-exclusive example, the voltagesource 132 is a high-voltage source capable of applying a DC voltagepotential to the first electrode 124 on the order of kilovolts (kV). Forexample, voltage potential (relative to ground) may be in a range (inabsolute value) from about 1000 V (1 kV) to about 30,000 V (30 kV). Thevoltage potential applied may be positive or negative, i.e., the rangemay be from about +1000 V to about +30,000 V or from about −1000 V toabout −30,000 V. The foregoing range is merely one example. Depending onthe embodiment, the voltage potential may be less than 1000 V or greaterthan 30,000 V. More generally, the voltage source 132 is capable ofapplying a DC or AC voltage to the first electrode 124 at a magnitude(or in the case of AC power, a peak-to-peak amplitude and frequency)that is sufficient or effective to strike and maintain a coronadischarge or plasma in the environment in which the first electrode 124and the tissue 108 are located.

In some embodiments, the first electrode 124 may include a (highly)curved feature configured to generate a region of elevated electricfield strength surrounding the first electrode 124. For example, thecurved feature may be a sharp or geometrically abrupt feature, such asan edge or a pointed tip, or a small-diameter wire. In the illustratedembodiment, the first electrode 124 is configured as an elongated rodthat terminates at a distal electrode tip 136. The first electrode 124,or at least a tip section thereof that terminates at the distalelectrode tip 136, may be tapered such that the distal electrode tip 136is sharp or pointed. Generally, a sharper distal electrode tip 136generates a stronger electric field at the distal electrode tip 136, ascompared to a more blunt geometry. Thus, the first electrode 124 may beconfigured as a needle or pin (e.g., a corona discharge needle). In someembodiments, the first electrode 124 may be coaxially surrounded by abody 140 (shown in cross-section in FIG. 1) composed of an electricallyinsulating material. The electrically insulating material may also be asufficiently thermally insulating material, or the body 140 may furtherinclude a thermally insulating material coaxially surrounding theelectrically insulating material. The insulating body 140 may beconfigured to be hand-held by a user. That is, the first electrode 124may be configured as a hand-piece that is held by a user like a pen.Alternatively, the insulating body 140 may be configured to be mountedto an automated device (e.g., a motorized stage or robot) as appreciatedby persons skilled in the art. Thus, depending on the embodiment thefirst electrode 124 may be movable relative to the tissue 108 in amanual or automated manner.

The second electrode 128 is typically configured to serve as acounter-electrode or ground plane. The second electrode 128 may bepositioned so as to cooperate with the first electrode 124 in definingthe location and spatial orientation of the electric field and plasmagenerated by the applied voltage. In some embodiments and asillustrated, the second electrode 128 is positioned on a side of thetissue 108 opposite to the first electrode 124. In other words, thetissue 108 is positioned between the first electrode 124 and the secondelectrode 128. In other embodiments, the second electrode 128 may bepositioned above the tissue 108, or juxtaposed at roughly the sameelevation as the tissue 108 relative to some reference plane. In theillustrated embodiment, the second electrode 128 has a thin planar(plate-shaped) geometry of greater planar area than that of the tissuesample 104, and the tissue sample 104 is placed onto the secondelectrode 128. As one non-limiting example, the second electrode 128 maybe a metallic (e.g., aluminum) foil. In other embodiments, the secondelectrode 128 may have an elongated rod-type geometry similar to theillustrated example of the first electrode 124. In various embodiments,more than one first electrode 124 and/or more than one second electrode128 may be provided.

In further embodiments, particularly when AC power is utilized, thesecond electrode 128 may coaxially surround the first electrode 124 suchthat an electrically insulating portion of the body 140 is interposedbetween the first electrode 124 and the second electrode 128. In thiscase, the second electrode 128 may in turn be coaxially surrounded byelectrically insulating and/or thermally insulating material, which maybe considered as being part of the schematically illustrated body 140.

The device 100 may include electronics that include the voltage source132 and other appropriate components. The electronics may include, forexample, an ON/OFF switch (not specifically shown) for controlling theapplication of voltage potential to the first electrode 116, a component(e.g., a control knob, not shown) configured for adjusting the level ofvoltage potential applied to the first electrode 116, etc. Some or allof the electronics may be arranged in a control console of the device100. In hand-held embodiments, the ON/OFF switch (or both the ON/OFFswitch and voltage level adjustment component) may be located at theinsulating body 140 so as to be easily accessible by the user.Alternatively, controls such as the ON/OFF switch and voltage leveladjustment component may be located at the control console or afoot-operated module.

The heating device 120 generally may have any configuration effectivefor generating and transferring heat energy to an upper heating surface144 of the heating device 120. Thus, for example, the heating device 120may include a body 148 containing one or more resistive heating elements(not specifically shown) in thermal contact with the heating surface144, and a voltage source (power supply) 152 providing electricalcurrent to the heating elements. Thus in the illustrated embodiment, thesecond electrode 128 is placed or mounted on the heating surface 144 ofthe heating device 120, and the tissue 108 and supporting substrate 112are in turn placed or mounted on the second electrode 128. In thepresent embodiment, the device 100, including the heating device 120,has an open architecture. Alternatively, the heating device 120 mayinclude chamber in which the first electrode 124, the second electrode128 and the heating surface 144 are positioned, and into which thetissue 108 and supporting substrate 112 are loaded. As an alternative toresistive heating elements, the heating device 120 may provide one ormore radiant heating sources such as infrared (IR) lamps.

FIG. 2 is a schematic elevation view of the tissue preparation device100, illustrating its operation. The tissue 108 and supporting substrate112 are positioned such that they are in thermal contact with theheating surface 144 of the heating device 120, such as by being placedon the second electrode 128. The heating device 120 is then activated togenerate and transfer heat energy 256 to the heating surface 144, andconsequently to the tissue 108 via heat conduction. A sufficient amountof heat energy 256 is deposited in the tissue 108 to melt the paraffinembedded therein, thereby rendering the paraffin readily flowable. Thetissue 108 may be heated to, for example, a temperature in a range ofabout 35° C. to about 70° C. More generally, the tissue 108 may beheated to the melting point of the paraffin, which falls within theforegoing range.

The electric field-generating device 116 is then activated to generatean electric field of a strength great enough to generate and sustain acorona discharge or plasma 260 in a region around the electrode tip 136of the first electrode 124, but not so great as to cause electricalarcing between the first electrode 124 and another object such as thesecond electrode 128. The electric field accelerates free electrons inthe air (or other gaseous medium) into collisions with neutrals (neutralatoms and molecules) in the air (or other gaseous medium). Some of thecollisions occur at a high enough energy to ionize the impactedneutrals, thereby liberating more electrons and leading to morecollisions between free electrons and neutrals. As long as the electricfield is present and of sufficient strength, the ionization eventscontinue in a chain-reaction effect termed an electron avalanche.Photons are also generated in the plasma 260 due to recombination eventsbetween electrons and positive ions, and contribute to ionization ofneutrals as well. The plasma 260 generated by the electricfield-generating device 116 generally is a mixture of charged particles(ions and electrons) and neutrals, as well as other energetic speciessuch as metastables and photons.

In some embodiments, the first electrode 124 has a positive polarityrelative to the second electrode 128. In this case, the plasma 260 maybe a positive corona discharge. Positive ions are repelled from thefirst electrode 124 and drawn toward the second electrode 128. On theother hand, negative ions are drawn toward the first electrode 124 andrepelled from the second electrode 128. Similarly, electrons are drawntoward the first electrode 124 and repelled from the second electrode128. In other embodiments, the first electrode 124 may have a negativepolarity relative to the second electrode 128, in which case the plasma260 may be a negative corona discharge.

In FIG. 2, the closed dashed line referred to herein as the plasma 260schematically depicts the outer spatial extent of the plasma 260 (or atleast the active plasma), which may also be referred to as theionization or plasma-forming region. Outside of this region (plasma260), the electric field is not strong enough to sustain plasma in theair (or other gaseous medium). In other words, plasma is extinguishedoutside of this region. It will be understood that the plasma 260 isdepicted schematically for illustrative purposes. In practice, theactual size and shape of the plasma 260 (e.g., cloud, plume, etc.) maydiffer appreciably from the schematic depiction shown in FIG. 2.

As depicted in FIG. 2, the energized first electrode 124 is positionedabove the tissue 108, and close enough to the tissue 108 that the tissue108 is exposed to the highly energetic plasma 260. Consequently, theenergetic species of the plasma 260 interact with the paraffin to ionizethe paraffin molecules. The paraffin ions (i.e., ionized paraffinmolecules) are repelled by charged species of the plasma 260 of the samepolarity (positive or negative), and by the first electrode 124 if thefirst electrode 124 has the same polarity as the ionized paraffin. Onthe other hand, the paraffin is attracted to oppositely charged speciesof the plasma 260, and to the first electrode 124 if also oppositelycharged. Hence, the first electrode 124 can be moved in any desireddirection across (over) the tissue 108 and the underlying substrate 112to move the paraffin by electrostatic force, i.e. by either chargerepulsion or attraction depending on the respective polarities of theionized paraffin and the first electrode 124, out from the tissue 108.Thus, movement of the first electrode 124 in a given direction willeither push or pull the ionized paraffin in the same general direction.As one non-limiting example, FIG. 2 depicts the first electrode 124being moved over (without contacting) the tissue 108 in the left-warddirection (from the perspective of FIG. 2), as indicated by a horizontalarrow 264. In this example, the first electrode 124 and the ionizedparaffin have the same polarity. The movement of the first electrode 124causes the ionized paraffin to be moved in the same left-ward direction,whereby the ionized paraffin leaves the confines of the tissue 108. FIG.2 also depicts a mass of ionized paraffin 268, having been separatedfrom the tissue 108, being moved away from the tissue 108 along thesurface of the substrate 112 in response to the movement of the firstelectrode 124 and the tip-localized energetic plasma 260 generatedthereby. In this example the ionized paraffin 268, still in a flowable(melted) state, flows in the left-ward direction as indicated by ahorizontal arrow 272.

A non-limiting example of a method for preparing a tissue will now bedescribed, using the example described above and illustrated in FIGS. 1and 2. A paraffin-embedded tissue 108 is provided. Providing the tissue108 may include various processing steps after initially acquiring thetissue 108 from the source, such as fixing, dehydration, alcoholremoval, paraffin infiltration/embedding, sectioning, etc. as describedherein. In this example, providing the tissue 108 includes positioning(placing or mounting) the tissue 108 on a solid substrate 112, andpositioning (placing or mounting) the tissue 108 (supported on thesubstrate 112) on or near a (second) electrode 128. Heat energy 256 isapplied to the tissue 108 as needed to melt the paraffin dispersed inthe tissue 108, i.e., to render the paraffin flowable. An electric fieldis applied that is effective to impart charge to the paraffin byionizing the paraffin and to move the ionized paraffin out from thetissue 108. In this example, the electric field is generated between afirst electrode 124 and the second electrode 128 by applying a voltagepotential to the first electrode 124. Further in this example, theelectric field applied is effective to generate plasma 260 in a regionextending at least between the electrode tip 136 of the first electrode124 and the tissue 108, whereby paraffin proximate to the electrode tip136 is exposed to the plasma 260. The first electrode 124 is moved inone or more directions relative to the tissue 108 as needed to move theionized paraffin out from the tissue 108. Typically, the first electrode124 is moved while the tissue 108 remains stationary. Alternatively oradditionally, the tissue 108 may be moved relative to the firstelectrode 124. The heat energy and the electric field are applied, andthe first electrode 124 is moved, for a duration sufficient to removeall (or substantially all) of the paraffin from the tissue 108. Thetotal duration required may be, for example, a few minutes (e.g., aboutfive minutes). In other words, the method may entail removingsubstantially all of the paraffin from the tissue.

Depending on the amount of time required to remove all (or substantiallyall) of the paraffin from the tissue 108, it may or may not be necessaryto continue to apply heat energy while the electric field is beingapplied and the first electrode 124 is being moved. The paraffin needsto be flowable to facilitate its movement out from the tissue 108.Accordingly, the heat energy should be applied for a period of time longenough to prevent the paraffin from re-solidifying during the removalprocess. Depending on the embodiment, the time period for heatapplication may or may not overlap with the time period for electricfield application.

After the paraffin has been removed from the tissue 108, a stainingprocess may be performed on the tissue 108. For example, the tissue 108may be stained with a standard staining agent such as hematoxylin andeosin (H&E), or an immunohistochemical (IHC) staining agent or otherspecial staining agent. Other desired processes may be performed on thetissue 108. For example, nucleic acids may be isolated from the tissue108 and subjected to further processing such as, for example,amplification by polymerase chain reaction (PCR), hybridization, etc.

From the foregoing, it is evident that the tissue preparation device 100and its method of use may provide a number of advantages. As noted abovein the background section of this disclosure, after paraffin-embeddedtissue has been sectioned into thin slices, the resulting tissuesections conventionally undergo a critical drying process that ensuresthe tissue sections are fully adhered to the slides (i.e., solidsubstrates 112) and thereby will not be lost during subsequent handlingor processing. The conventional drying process may take an hour or so tocomplete. By comparison, the tissue preparation device 100 is effectivein removing water from the tissue as well as paraffin. The tissuepreparation device allows better adhesion to both non-charged andcharged slides than the conventional drying process. Thus, theconventional drying process may be eliminated, which consequently maysave nearly an hour or so from the total processing time of the tissue.Accordingly, the tissue preparation device 100 is effective forminimizing drying time while achieving tissue adhesion to the slide, Asalso noted above, after drying the tissue and before initiating thestaining process, the paraffin must be removed from the tissue, whichconventionally is performed by dipping the tissue slide in xylene todissolve the paraffin. The electric field-based deparaffinizationprocess of the present disclosure removes most or substantially all ofthe paraffin, which minimizes or eliminates the use of xylene fordeparaffinization, which is highly desirable given that xylene is atoxic chemical.

Moreover, the electric field-based deparaffinization process of thepresent disclosure has been found to be compatible with not onlystandard hematoxylin and eosin (H&E) staining, but also antigenretrieval and staining for immunohistochemistry (IHC).

Furthermore, because xylene-based deparaffinization is minimized oreliminated and accordingly a cause of oxidative damage to guanosinenucleotides is minimized or eliminated, the electric field-baseddeparaffinization process of the present disclosure may enable andpromote the ability to extract nucleic acids (DNA and RNA) of superiorquality from tissues. Since tumor tissue may comprise only a portion ofa section and only the tumor portion is typically selected forsubsequent genomic analysis, multiple sections are routinely cut toobtain sufficient material. The electric field-based deparaffinizationprocess may allow thicker sections to be cut and sufficiently cleared ofparaffin to be compatible with genomic analysis kits.

Paraffin removal as described herein may conveniently be carried outunder ambient conditions. Ambient air may be utilized as aplasma-forming gas mixture. That is, the plasma utilized may be an airplasma. In other embodiments, the plasma-forming process may be enhancedby providing a flow of one or more specific plasma-forming gases to theionization (plasma-forming) region in the vicinity of the firstelectrode. Examples of specific plasma-forming gases include, but arenot limited to, diatomic oxygen (O₂), diatomic nitrogen (N₂), a noblegas such as argon (Ar), etc. A specific plasma-forming gas may beprovided by nozzles configured to direct the gas to the ionizationregion where the gas can be excited by the applied electric-field.Alternatively, the device 100 and the tissue 108 may be positioned in anenclosure that provides a controlled environment (relative to theambient), and the plasma-forming gas may be flowed into the enclosure.The use of specific plasma-forming gas(es) to modify the composition ofthe air in the ionization region, or instead or air, may be desired fortuning the conditions (e.g., voltage parameters) under which plasma isgenerated and sustained, for ensuring that the paraffin is ionizedpreferentially over other components of the tissue 108 that do not needto be ionized, etc.

Thus far, the mechanism or technique of ionization has been describedprimarily in the context of a corona discharge-type plasma. Thepresently disclosed subject matter in its broader aspects, however, isnot limited to any specific mechanism of ionization. More generally, anytype of ionization suitable for the process of paraffin removal may beutilized. Typically, atmospheric-pressure ionization (API) techniquesare contemplated as they do not require operating in an evacuatedenvironment. Examples of API techniques include, but are not limited to,atmospheric-pressure plasma-based ionization, atmospheric-pressurechemical ionization (APCI), atmospheric-pressure photoionization (APPI)(e.g., using a laser, ultraviolet lamp, etc.), inductively coupledplasma (ICP) ionization, microwave induced plasma (MIP) ionization,dielectric barrier discharge (DBD) plasma ionization, etc.Alternatively, ionization in a vacuum regime may be carried out if thedevice 100 and the tissue 108 are positioned in an appropriatelyconfigured vacuum chamber. Examples ionization techniques performed invacuum include, but are not limited to, glow discharge (GD) ionization,electron ionization (EI) using a filament for thermionic emission, andchemical ionization (CI) using a filament for thermionic emission.

FIG. 3 is a schematic view of a tissue preparation device 300 accordingto another embodiment. Similar to the embodiment described above andillustrated in FIGS. 1 and 2, the device 300 includes an electricfield-generating device 316 and a heating device 320 on which asupported tissue arrangement 304 (paraffin-impregnated tissue 308 on,for example, a microscope slide 312) is supported. In the presentembodiment, the electric field-generating device 316 includes aplurality of movable first electrodes 324. The first electrodes 324 maybe arranged in a one-dimensional or two-dimensional array. The firstelectrodes 324 may be spaced from each other by a fixed distance (orpitch). The first electrodes 324 may be (removably) mounted to anappropriately configured electrode support 376 that determines thepositions and spacing of the first electrodes 324 relative to eachother. In some embodiments, the electrode support 376 may beelectrically conductive to minimize the amount of electrical wiring 380needed between the first electrodes 324 and a voltage source (electricalpower supply) 332. The electric field-generating device 316 may furtherinclude electrically insulating and/or thermally insulating structures(not shown) attached to or otherwise mechanically referenced to theelectrode support 376 and/or the first electrodes 324 as needed tofacilitate manual or automated movement of the first electrodes 324across the tissue 308. For example, electrically insulating and/orthermally insulating structures may be provided in the form of auser-graspable handle or a fixture configured for coupling to amotorized stage or robot. Also in the illustrated example, the voltagesource 332 is provided in a control console that includes user-operatedcontrol knobs for adjusting voltage, or both voltage and frequency inthe case of an AC voltage source.

The multiple first electrodes 324 may be useful for increasing theoverall size or footprint of the active region of plasma 360 generatedby the electric field-generating device 316. In this case, the plasma360 may be shaped as a wide curtain. The device 300 may otherwisegenerally be configured and operated similarly to the device 100described above and illustrated in FIGS. 1 and 2.

One or more second electrodes (not specifically shown) utilized as acounter-electrode or ground electrode may be disposed on or integratedwith the heating device 320, or otherwise positioned proximate to thetissue 308.

As further shown in FIG. 3, the device 300 (or any of the otherembodiments of the tissue preparation device disclosed herein) mayinclude a paraffin collection device 306 utilized to collect theparaffin as it is removed from the tissue 308. The paraffin collectiondevice 306 may be movable, or its position adjustable, relative to theheating surface of the (main) heating device 320. In some embodiments,the paraffin collection device 306 may be composed of a thermallyconductive material and in operation may be heated to assist in theparaffin removal. Accordingly, the paraffin collection device 306 mayalso be referred to herein as a second heating device. The paraffincollection device 306 may be utilized, for example, to assist in“wicking away” the paraffin as the paraffin is moved (“pushed” or“pulled,” or repelled or attracted, as described herein) to one side ofthe substrate 312 (the left side in FIG. 3). For this purpose, theparaffin collection device 306 may be heated to (operate at) a highertemperature than that of the heating surface of the (main) heatingdevice 320 (and the paraffin) to cause the paraffin to readily flow ontothe paraffin collection device 306 as the paraffin reaches the end ofthe substrate 312.

FIG. 4 is a schematic view of a tissue preparation device 400 accordingto another embodiment. Similar to other embodiments described herein,the device 400 includes an electric field-generating device 316 and aheating device 420 near which a supported tissue arrangement 404 ispositioned. By way of example, the electric field-generating device 316with multiple first electrodes 324 described above is also provided inthe present embodiment, although any of the other electricfield-generating devices described herein may be included in the tissuepreparation device 400. In the present embodiment, aparaffin-impregnated tissue 408 is supported on a solid substrate in theform of a porous frit 412, which may be made of glass or other materialcapable of withstanding the heat applied during tissue removal. The frit412 may be removably mounted in a liquid container 484 (e.g., column,vial, test tube, vessel, flask, well of a microtiter plate, etc.) suchas at or near the open top of the container 484. The container 484 maybe removably mounted in an opening 488 of a container support 492 (e.g.,a support plate with one or more openings). The container support 492may include an array of openings 488 for supporting respectivecontainers 484 and corresponding tissues 408 and fits 412.

In the present embodiment, all or part of the heating device 420 may beintegrated with the container support 492. For example, the heatingdevice 420 may include a plurality of circumferentially spaced (relativeto the longitudinal axis of the container support 492) heating elementspositioned on or in the container support 492 in close enough proximityto the tissue sample 404 to be in thermal contact with the tissue 408.In the present context, the term “in thermal contact” generally may betaken to mean that the heating elements are positioned close enough tothe tissue 408 such that when they are activated they establish athermal gradient effective for transferring an amount of heat to thetissue 408 needed to melt the tissue 408 within a short period of time,for example within a minute or a few minutes.

One or more second electrodes (not specifically shown) utilized as acounter-electrode or ground electrode may be disposed on or integratedwith the heating device 420, or otherwise positioned proximate to thetissue 408.

In the present embodiment, as the paraffin is removed from the tissue408 by the moving first electrodes 324, the paraffin may drain throughthe holes or pores of the frit 412 and be collected in the container484. The tissue sample 404 (deparaffinized tissue 408 and frit 412) maythen be placed in another container for further processing as needed. Insome embodiments, the container 484 may include an opening 496 at itsbase to allow the paraffin to drain out from the container 484.

In other embodiments of tissue samples, the tissue may be disposeddirectly on a surface of a liquid container (e.g., column, vial, testtube, vessel, flask, well of a microtiter plate, etc.), in which casethe liquid container serves as the solid support for the tissue.

In the embodiments described and illustrated thus far, the tissue (andunderlying substrate, if provided) have been depicted as beinghorizontally oriented. However, the tissue (and underlying substrate, ifprovided) may be oriented vertically (ninety degrees relative to ahorizontal reference plane) or at any angle between the horizontal andvertical reference planes (in a range from zero degrees to ninetydegrees relative to a horizontal reference plane). Orienting the tissueat an angle to the horizontal may enhance paraffin removal through theassistance of gravity.

Various other embodiments of a tissue sample preparation deviceencompassed by the present disclosure may include combinations offeatures from different embodiments described above.

EXEMPLARY EMBODIMENTS

Exemplary embodiments provided in accordance with the presentlydisclosed subject matter include, but are not limited to, the following:

1. A method for preparing a tissue, the method comprising:

providing a tissue embedded with paraffin; and

removing the paraffin from the tissue without adding any liquid to thetissue, wherein removing the paraffin renders the tissue substantiallyfree of paraffin.

2. The method of embodiment 1, wherein removing the paraffin from thetissue without adding any liquid to the tissue comprises:

applying heat energy to the tissue effective to melt the paraffin;

applying an electric field effective to ionize the paraffin and to movethe ionized paraffin out from the tissue due to electrostatic force; and

continuing to apply the electric field until the tissue is substantiallyfree of paraffin.

3. A method for preparing a tissue, the method comprising:

providing a tissue embedded with paraffin;

applying heat energy to the tissue effective to melt the paraffin;

applying an electric field effective to ionize the paraffin and to movethe ionized paraffin out from the tissue due to electrostatic force; and

continuing to apply the electric field until the tissue is substantiallyfree of paraffin.

4. The method of any of the preceding embodiments, wherein providing thetissue comprises placing the tissue on a solid substrate.

5. The method of embodiment 4, wherein the solid substrate is selectedfrom the group consisting of a slide, a plate, a frit, beads, a porousmedium, a filter, and a liquid container.

6. The method of embodiment 4 or 5, wherein the solid substratecomprises a substrate surface contacting the tissue, and the substratesurface has a higher surface energy than the paraffin.

7. The method of any of embodiments 2-6, wherein the applying heatenergy is performed by one selected from the group consisting of:

placing the tissue sample on a surface and heating the surface;

placing the tissue sample in a chamber and heating the chamber;

applying radiant heat energy;

applying infrared radiation; and

a combination of two or more of the foregoing.

8. The method of any of embodiments 2-7, wherein the applying heatenergy comprises heating the paraffin to a temperature in a range fromabout 35° C. to about 70° C.

9. The method of any of embodiments 2-8, wherein the electric field is aDC electric field.

10. The method of any of embodiments 2-8, wherein the electric field isan AC electric field.

11. The method of any of embodiments 2-10, comprising applying theelectric field so as to produce a plasma in an ionization region towhich the paraffin is exposed.

12. The method of embodiment 11, wherein the plasma is produced from airmolecules.

13. The method of any of embodiments 2-12, wherein applying the electricfield comprises applying a voltage between a first electrode and asecond electrode.

14. The method of embodiment 13, wherein the voltage has an absolutevalue in a range from about 1000 V to about 30,000 V.

15. The method of embodiment 13 or 14, wherein applying the electricfield produces a corona discharge in a region surrounding the firstelectrode, and further comprising positioning the first electrode so asto expose the paraffin to the corona discharge.

16. The method of any of embodiments 13-15, wherein the first electrodecomprises a curved feature configured to generate a region of elevatedelectric field strength surrounding the first electrode.

17. The method of embodiment 16, wherein the curved feature comprises anedge or a tip of the first electrode.

18. The method of any of embodiments 13-17, wherein the second electrodeis a planar electrode.

19. The method of any of embodiments 13-18, comprising electricallygrounding the second electrode while applying the electric field.

20. The method of any of embodiments 13-19, comprising moving at leastone of the first electrode and the tissue relative to the other, in adirection that moves the paraffin away from the tissue.

21. The method of any of embodiments 13-20, wherein the first electrodecomprises an array of electrodes.

22. The method of any of embodiments 13-21, wherein the tissue ispositioned between the first electrode and the second electrode.

23. The method of any of the preceding embodiments, wherein providingthe tissue comprises positioning the tissue in or above a container, andfurther comprising collecting the paraffin in the container after movingthe paraffin out from the tissue.

24. The method of any of embodiments 2-23, comprising moving at leastone of the electric field and the tissue relative to the other, in adirection that moves the paraffin away from the tissue.

25. The method of any of embodiments 2-24, comprising applying the heatenergy while applying the electric field.

26. The method of any of the preceding embodiments, comprising stainingthe tissue after removing the paraffin.

27. The method of embodiment 26, wherein staining the tissue comprisesstaining with an immunohistochemical staining agent.

28. The method of any of the preceding embodiments, comprising isolatingnucleic acids from the tissue after removing the paraffin.

29. The method of any of the preceding embodiments, wherein afterremoving the paraffin from the tissue, or after applying the electricfield, the tissue is greater than 98% free of paraffin.

30. A method for preparing a tissue, the method comprising:

providing a tissue embedded with paraffin; and

removing substantially all of the paraffin from the tissue withoutadding any liquid to the tissue.

31. The method of embodiment 30, wherein removing substantially all ofthe paraffin from the tissue removing greater than 98% of the paraffin.

32. The method of embodiment 30, wherein after removing substantiallyall of the paraffin from the tissue, the tissue contains residualparaffin, and the residual paraffin is less than 2% of the paraffinoriginally contained in the tissue prior to the step of removing.

33. A tissue preparation device, comprising an electric field-generatingdevice configured for applying the electrical field according to themethod of any of the preceding embodiments.

34. The tissue preparation device of embodiment 33, comprising a heatingdevice configured for applying the heat energy.

35. A tissue preparation device, comprising:

a heating device configured for applying heat energy to a tissueeffective to melt paraffin embedded in the tissue; and

an electric field-generating device configured for applying anelectrical field effective to ionize the paraffin and to move theionized paraffin out from the tissue due to electrostatic force.

36. The tissue preparation device of embodiment 35, wherein the electricfield-generating device is configured for applying the electric fieldeffective to produce plasma in an ionization region to which theparaffin is exposed.

37. The tissue preparation device of embodiment 35 or 36, wherein theelectric field-generating device comprises a first electrode and asecond electrode, and the electric field-generating device is configuredfor applying the electric field between the first electrode and thesecond electrode.

38. The tissue preparation device of embodiment 37, wherein the firstelectrode comprises a curved feature configured to generate a region ofelevated electric field strength surrounding the first electrode.

39. The tissue preparation device of embodiment 37 or 38, wherein thefirst electrode is configured for being moved relative to the tissue.

It will be understood that terms such as “communicate” and “incommunication with” (for example, a first component “communicates with”or “is in communication with” a second component) are used herein toindicate a structural, functional, mechanical, electrical, signal,optical, magnetic, electromagnetic, ionic or fluidic relationshipbetween two or more components or elements. As such, the fact that onecomponent is said to communicate with a second component is not intendedto exclude the possibility that additional components may be presentbetween, and/or operatively associated or engaged with, the first andsecond components.

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation—the inventionbeing defined by the claims.

1.-19. (canceled)
 20. A tissue preparation device, comprising: a heatingdevice configured for applying heat energy to a tissue effective to meltparaffin embedded in the tissue; and an electric field-generating deviceconfigured for applying an electrical field effective to ionize paraffinand to move the ionized paraffin out from the tissue.
 21. The tissuepreparation device of claim 20, wherein the electric field-generatingdevice comprises a first electrode and a second electrode.
 22. Thetissue preparation device of claim 21, wherein the electricfield-generating device produces a corona discharge in a regionsurrounding the first electrode.
 23. The tissue preparation device ofclaim 21, wherein the first electrode has a configuration selected fromthe group consisting of: a curved feature configured to generate aregion of elevated electric field strength surrounding the firstelectrode; and an edge or tip configured to generate a region ofelevated electric field strength surrounding the first electrode. 24.The tissue preparation device of claim 21, wherein the second electrodeis a planar electrode.
 25. The tissue preparation device of claim 21,wherein the first electrode comprises an array of electrodes.
 26. Thetissue preparation device of claim 21, wherein the first electrode iscoaxially surrounded by an electrically insulating body.
 27. The tissuepreparation device of claim 26, wherein the electrically insulating bodyis configured to be hand-held by a user.
 28. The tissue preparationdevice of claim 26, wherein the electrically insulating body is mountedto a motorized stage or robot.
 29. The tissue preparation device ofclaim 21, wherein the first electrode is configured for movementrelative to the second electrode.
 30. The tissue preparation device ofclaim 21, wherein the second electrode is a counter-electrode or groundplane.
 31. The tissue preparation device of claim 21, wherein the secondelectrode has a thin planar geometry
 32. The tissue preparation deviceof claim 21, wherein the second electrode has an elongated rod-typegeometry.
 33. The tissue preparation device of claim 21, wherein thesecond electrode coaxially surrounds the first electrode, and anelectrically insulating body is interposed between the first electrodeand the second electrode.
 34. The tissue preparation device of claim 33,wherein the second electrode is coaxially surrounded by an electricallyinsulating and/or thermally insulating material.
 35. The tissuepreparation device of claim 20, further comprising a voltage source forsupplying a voltage potential to the electric field-generating device.36. The tissue preparation device of claim 20, further comprising acontroller that controls the application of voltage to the electricfield-generating device or the level of voltage applied to the electricfield-generating device.
 37. The tissue preparation device of claim 20,wherein the heating device comprises a resistive heating element. 38.The tissue preparation device of claim 20, wherein the heating devicecomprises a radiant heating source.
 39. The tissue preparation device ofclaim 20, wherein the electric field-generating device produces a plasmain an ionization region to which the paraffin is exposed.
 40. The tissuepreparation device of claim 20, wherein the first electrode comprises aneedle or pin.
 41. The tissue preparation device of claim 21, whereinthe first and second electrodes are positioned in a chamber configuredto receive a tissue on a supporting substrate.
 42. The tissuepreparation device of claim 20, wherein the paraffin-embedded tissue ismounted or freely resting on a substrate, such as a glass slide, aplate, a frit, a porous medium, a filter or a container.
 43. The tissuepreparation device of claim 42, wherein the substrate has a highersurface energy than the paraffin.
 44. The tissue preparation device ofclaim 42, wherein the tissue, substantially free of paraffin, adheres tothe substrate.
 45. The tissue preparation device of claim 42, whereinthe container is selected from the group consisting of a column, vial,test tube, vessel, flask and a well of a microtiter plate.
 46. Thetissue preparation device of claim 39, wherein the plasma is formed fromair, oxygen, nitrogen or a noble gas such as argon.
 47. The tissuepreparation device of claim 20, further comprising a paraffin collectiondevice.
 48. The tissue preparation device of claim 42, wherein thedevice may be oriented horizontally, vertically or at any angle relativea horizontal reference plane.
 49. A tissue preparation device comprisinga heating device and an electric field generating device which producestissue substantially free of paraffin and which is subsequently stableat room temperature for an extended period of time.
 50. The tissuepreparation device of claim 49, wherein the tissue is stable at roomtemperature overnight.